A conventional thin film formation apparatus comprises, as shown in FIG. 9, at least a printing roll 3 having a elastic letterpress 31 of resin or rubber fitted at a part of a surface of a cylinder part 30, and an intaglio roll (Anilox roll) 4 rotating while facing the printing roll 3, thereby transferring ink to a surface of the elastic letterpress 31 through contact with the printing roll 3. In the apparatus of such constitution, ink is transferred to a surface of a body to be printed (plate glass, plastic plate, film that can be wound in a roll, etc.) by pressing the elastic letterpress 31 into contact with the body to be printed, so as to form a thin film by printing.
In such thin film formation apparatus, while the cylinder part 30 of the printing roll 3, specifically a part without the elastic letterpress 31, and a non-printing image part never came into contact with the intaglio roll 4 (with reference to FIG. 12A), a printing image part of the letterpress 31 of the printing roll 3 is brought into contact with the intaglio roll 4 (referring to FIGS. 7, 12B). Contact is also maintained in a driving system, for example, between pinions of rotary shafts 6 of the intaglio roll 4 and the printing roll 3.
A primary usage of the thin film formation apparatus is to form liquid crystal orientation films in a process for production of electronic components such as display panels of liquid crystal display devices, etc. Although the liquid crystal orientation film of the display panel is naturally required to be uniform in thickness, the display panel increasingly has become larger in size and ofhigher image quality, and accordingly film thickness uniformity with higher accuracy is demanded.
Meanwhile, a drive environment for the thin film formation apparatus permits only an expensive clean room to avoid minute dust during forming the thin films such as liquid crystal orientation films or the like. The thin film formation apparatus is therefore required to be compact and light-weight in order to economically assure use of a space in the clean room that is as small as possible.
On the other hand, in order to form thin films of high accuracy, it is necessary that a resin liquid as the ink has a viscosity as low as 50-100 cp in comparison with a flexographic ink, a thin elastic letterpress is used to secure size accuracy thereof, and it is necessary to compensate for rattling and bending of rotary shafts of the printing roll and the intaglio roll. As such, a contact pressure between the elastic letterpress and intaglio roll is generally large compared with that in the case of flexography, and thereby it is necessary to transfer uniformly the ink from an ink hold part of the intaglio roll to the elastic letterpress. The contact pressure is measured by the amount of the letterpress 31 is pressed by the intaglio roll 4 (referring to FIG. 7). The "pressed amount" is a difference of thickness of the elastic letterpress 31 between when the printing image part of the letterpress 31 is not pressed by a surface of the intaglio roll 4 and when the printing image part of the letterpress 31 is depressed by the intaglio roll 4.
The above-described requirements lead to the following problems.
During the rotation of the printing roll 3 and intaglio roll 4, a contact state (referring to FIGS. 7, 12B) and a non-contact state (referring to FIG. 12A) are alternatively brought about between the elastic letterpress 31 and intaglio roll 4. Because of the large contact pressure between the letterpress 31 and intaglio roll 4 exerted during the contact state, the intaglio roll 4 collides sideways to the printing image part of the letterpress 31 when the non-contact state is changed to the contact-state, that is when the surface of the intaglio roll 4 rides over the surface of the elastic letterpress 31 (referring to FIG. 12B). Impacts and reaction from the elastic letterpress 31 at this time are transmitted to the rotary shafts 6 of the printing roll 3 and intaglio roll 4, which in turn vibrates the printing roll 3 and intaglio roll 4 due to a play of bearings 5 or play 100 between the rotary shafts 6 and inner rings of the bearings (referring to FIGS. 9, 10). Microscopically, the printing roll 3 and intaglio roll 4 rotate in the state of contact with each other. The printing roll 4 prints while in contact with the body to be printed.
When the letterpress 31 of the printing roll 3 and intaglio roll 4 are turned from the non-contact state to the contact state, in other words when the surface of the intaglio roll 4 rides over the surface of the letterpress 31, the printing roll 3 including the cylinder part 30 and the intaglio roll 4 are undesirably bent and, as a reaction to such bending, the printing roll 3 and intaglio roll 4 are vibrated. In consequence, microscopically the printing roll 3 and intaglio roll 4 rotate while bending and in contact with each other. The printing roll 3 while bending performs printing on the body to be printed (referring to FIG. 10).
As a result, stripe patterns (where the amount of ink transferred or thickness of a film formed by ink is alternately changed from large to small) are formed at the letterpress 31 and the body to be printed, at positions spaced in an axial direction of the roll.
Therefore, the present invention is devised to avoid the above-described disadvantages, and has for its object to provide a thin film formation apparatus capable of forming thin films of uniform thickness.